Answer: The answer is 80%.
Step-by-step explanation: Let us define the following events.
B = the event that the shirt is blue,
G = the event that the shirt is green
and
S = the event that the shirt is striped.
So, n(B) = 8, n(G) = 7, n(B and S) = 5, n(G and S) = 4.
n(S) = 5 + 4 = 9.
We have

Therefore, the required probability is

Thus, the answer is 80%.